The present invention pertains to a device for positioning and applying tension to a workpiece, such as trouser fabric during advancement thereof to the stitching instrumentalities of a sewing unit. A well known and common form of sewing unit is that of table-like structure having a sewing or work surface with a sewing machine mounted adjacent one end of said surface. The sewing machine includes the usual stitching and feeding elements, and the unit is provided with one or more tensioning devices defining traveling grippers having movable jaws for gripping and releasing the workpiece in timed sequence with the sewing cycle. The grippers are attached to cable-like elements that are effective in holding the workpiece taut and for returning said grippers to their starting position upon completion of the sewing cycle. The grippers also include adjustable positioning members mounted on the work surface for locating said grippers in their starting positions. The cable-like elements connected to the grippers are adapted to extend through central openings in the positioning members and their opposite ends are attached to counter-weights which serve to return said grippers to their starting positions upon release from the workpiece. The tension device is operatively associated with a feeder device of known type, and is adapted to locate a workpiece in a predetermined location for attachment of the grippers thereto upon their return to their respective positioning members located in starting position. The ability to continuously locate a gripper or grippers in the same starting position relative to the length of a workpiece to be gripped thereby presents a serious problem with tension devices that are adapted to move unrestricted with a workpiece along the work surface. Locating devices are available for the known types of sewing units and are effective in orienting the traveling grippers, upon return to their positioning members, to a position for engaging the next workpiece prior to commencement of another stitching cycle. These locating devices are considered rather complex, require a large number of interconnected elements to accomplish their intended function, and require separate and costly electro-pneumatic control circuits for their operation.
In the case of an additional tensioning device for gripping the workpiece intermediate the ends thereof, utilization of the available locating devices would be practically impossible due to the great number of additional interconnected elements that would be required. Additionally, difficulty would be encountered in attempting to interconnect its operating circuit with that of the end tensioning device for the sequence of operation of both devices differ within the range of the total operating cycle of the sewing unit.
An object of the present invention is to provide a traveling gripper positioning device for sewing units which is of simplified construction, inexpensive to manufacture and which will consistently and accurately perform its intended function.
A more specific object is that of providing a positioning device for an intermediate traveling gripper which is capable of functioning independently of and without operatively interfering with the positioning device for the gripper which holds the end of a workpiece.
The technical problem to be solved in order to achieve the above-mentioned objects is that of eliminating the electropneumatic controls for the locating devices. The solution to this technical problem is accomplished by means of gripper return devices which upon return of a gripper to its starting position, is effective in causing pivotal movement of said gripper which orients it to a predetermined position and in readiness for attachment to the next workpiece.